The role of covalency in the orbital-order of 3d1 perovskites

We investigate the interplay between lattice distortion, bond formation and orbital ordering in ATiO3ATiO3 (A=LaA=La, Y) perovskites using full-potential density-functional calculations and ELF analysis. It is shown that the lattice distortion implies a dramatic reorganization of the bonds between A cations and oxygen on the one hand, and titanium and oxygen on the other hand. Along the series cubic LaTiO3, orthorhombic LaTiO3, orthorhombic YTiO3 an increasing asymmetrization of the environment of Ti is taking place.We show that changes in chemical bonding are relevant for lifting the degeneracy of Ti 3d orbitals across the metal–insulator transition and we sketch the use of the ELF to visualize orbital ordering.

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